The present invention relates generally to stacked die semiconductor packaging and, more particularly, to a stacked die package having a sensor die.
Packaged semiconductors provide external electric connections and physical protection for packaged dies. Continued progress in reduction of the size of the semiconductor dies, and increased functionality of the circuits integrated in the dies, requires size reduction of the packaging with the same or greater number of external electrical connectors.
One typical type of semiconductor package is a Quad Flat Pack (QFP), which is formed with a semiconductor die mounted to a lead frame. The lead frame is formed from a sheet of metal that has a die attach pad often called a die paddle or die flag and arms or tie bars that attach the flag to a frame. Lead fingers of the lead frame are wire bonded to bonding pads the die to provide a means of easily electrically connecting the die to circuit boards and the like. After the die bonding pads and the lead fingers are wire bonded, the semiconductor die and bond wires are encapsulated with a plastic material leaving only sections of the lead fingers exposed. These exposed leads are cut from the frame (singulated) and bent for ease of connection to a circuit board.
When sensors such pressure sensors used in tire pressure monitoring systems are packaged, the mounting surface area (footprint) may increase by at least the area of the active surface of the sensors. Stacking of a die and sensor in a semiconductor package can reduce the mounting surface area. However, the active surface of the sensor must face away from the mounting surface in order to properly function. Furthermore, the sensor (sensor die) cannot easily be encapsulated with the plastics material together with the other dies in the package, in a single molding step, as the sensor die is sensitive to stress induced by conventional molding processes. Therefore, it would be advantageous to have an efficient and economical method to package a sensor die with other semiconductor dies.